Seeing as it's about regs, you all have to work to BS 7671 (as you all know !-) )
The new ones out now and comes into force in a few weeks.
Just a heads up for the peeps who don't know all the changes, the main one that affects you lot is that all cables in all environments that are mounted in a escape routes now have to have metal fixings, even a door bell cable clipped across a front door in someone's house.